A class action lawsuit can help people similarly harmed by a corporation, or another party, such as a product manufacturer or developer, a lending or other financial institution, or an insurance company. An individual may have been injured or suffered some other damage, but one person's damage alone might not be great enough to justify the expenses of a lawsuit, especially against a large company. The wrongdoer in such a circumstance may get away with its wrong due to costs associated with investigating and filing a lawsuit. But, if enough people were injured, then the combined damages may be enough to justify bringing a lawsuit to hold the wrongdoer responsible for the harm caused.

A class action empowers people to effect change for an entire group of people harmed by the same or similar practices. A class action is a civil lawsuit where one or more complainants, also referred to as class representatives, sue on behalf of a class of people with common injuries. Initially, the judge will have to determine whether the claims of the class representatives arise from facts or law that are common to the class members, typically referred to as the commonality issue.

Most class actions are called plaintiff class actions because the parties who are suing are called the plaintiffs; however, there are also class actions called defendant class actions because a class action can be filed against one or more defendants representing a group of defendants.